Vibrational Behavior of Water Adsorbed on Forsterite
(Mg2SiO4) Surfaces
Posted on 2020-06-26 - 18:08
The
dynamics of water on or in a mineral substrate plays an important
role in interfacial processes. This is because the structure and dynamics
of interfacial water deviate from those of bulk water due to the change
of interactions between surface water molecules and the interactions
between the surface water and the substrate. This work presents a
study of the vibrational behavior of water on a forsterite (Mg- end
member of olivine) surface using inelastic neutron scattering (INS)
and molecular dynamics (MD) simulations as complementary tools. The
synthetic nano-forsterite used (dominated by the (010) crystal face),
i.e., “dry” sample, inherently has a partial hydration/hydroxylation
layer on the surface, as shown by previous studies and TGA. In the
INS experiments, three water loadings (0.5, 1, and 2 monolayers) were
added to the nano-forsterite surfaces. For samples with lower water
loadings, i.e., dry and 0.5 monolayers, the INS spectra exhibited
a red shift (lower frequency) of the water libration band and strengthening
(blue shift, higher frequency) of the O–H stretching modes,
implying weakening of the hydrogen bonding acting on the water molecules.
In the simulations, we modeled the forsterite (010) surface and titrated
it with two water loadings representing the lower and higher experimental
water loadings. The lower loading in the simulation is equivalent
to the dry and 0.5 monolayer samples in the experiment, thus suggesting
weak hydrogen bonding between water molecules. The higher-loading
simulation emulates the multilayer adsorption experiment. This produced
a more significant shift of the vibrational bands, implying increased
hydrogen-bonding strength and disorder between water molecules. The
MD simulations complement the INS study by providing a detailed interfacial
structure, and the combination of the two approaches provides a fundamental
understanding of how the presence of the olivine surface impacts the
vibrational behavior of water under different degrees of hydrationa
phenomenon widely associated with terrestrial and extraterrestrial
surfaces and near-surface processes.
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Liu, Tingting; Gautam, Siddharth S.; Daemen, Luke L.; Kolesnikov, Alexander I.; Anovitz, Lawrence M.; Hartl, Monika; et al. (2020). Vibrational Behavior of Water Adsorbed on Forsterite
(Mg2SiO4) Surfaces. ACS Publications. Collection. https://doi.org/10.1021/acsearthspacechem.0c00084
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AUTHORS (7)
TL
Tingting Liu
SG
Siddharth S. Gautam
LD
Luke L. Daemen
AK
Alexander I. Kolesnikov
LA
Lawrence M. Anovitz
MH
Monika Hartl
DC
David R. Cole